Meaning: Correct someone when they say something wrong
Example: My teacher PICKS UP ON any mistake I make and corrects me.
Meaning: Notice something that most people don't
Example: He's very quick to PICK UP ON new trends.
Meaning: React to something
Example: The government has PICKED UP ON the reports in the media.
Meaning: Comment on something said earlier in a conversation
Example: I'd like to PICK UP ON the point that Jill made.